Heat stable reaction injection molded elastomers

ABSTRACT

The invention is a method for making reaction injection molded polyurethane of improved properties. The product comprises the cured reaction product of a high molecular weight polyhydric polyether, a low molecular weight active hydrogen containing compound of at least two functionality and a polyisocyanate. The reaction product is cured by subjecting it to an ambient temperature of from about 290°-425° F. for a time sufficient to achieve an improvement in properties. The invention is also the resulting polyurethane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns the field of reaction injection moldedpolyurethanes.

2. Description of the Prior Art

Reaction Injection Molding (RIM) is a technique for the rapid mixing andmolding of large, fast curing urethane parts. RIM polyurethane parts areused in a variety of exterior body applications on automobiles wheretheir light weight contributes to energy conservation. RIM parts aregenerally made by rapidly mixing active hydrogen containing materialswith polyisocyanate and placing the mixture into a mold where reactionproceeds. After reaction and demolding, the parts may be subjected to anadditional curing step which comprises placing the parts in an ambienttemperature of about 250° F. Indeed, the standard industry practice hasbeen to post cure RIM parts at 250° F. The article "Processing andProperties of a Microcellular Foam System with Low Sensitivity toTemperature", Robert L. McBrayer and Gary J. Griffin, Journal ofCellular Plastics, July through August 1977, reveals temperatures up to300° F. However, the article indicates that temperatures greater than250° F. may not be practical due to part distortion. U.S. Pat. No.4,098,773 refers to heating RIM elastomers in the reaction mold withoutwaiting for the reaction to complete at temperatures ranging from 212°F. to 392° F. The patent states that preferably this curing/reactingtemperature is from 212° F. to 300° F. However, in the only exampleswhere parts were actually heated in this manner, temperatures of only212° and 248° F. were used.

It has been surprisingly discovered that RIM polyurethane parts may bepost cured at temperatures well above 300° F. and that a substantialimprovement in properties takes place due to the high post curingtemperature.

SUMMARY OF THE INVENTION

The invention is a method for making reaction injection molded (RIM)polyurethane of improved properties wherein polyhydric polyethers ofabove about 1000 molecular weight, a chain-extender comprising lowmolecular weight active hydrogen containing compound of at least twofunctionality and a polyisocyanate is post cured at an ambienttemperature of from about 290° to 425° F., preferably about 310° F. to350° F., for a length of time sufficient to achieve an improvement inproperties. The invention is also the resulting RIM polyurethane parts.

BRIEF SUMMARY OF THE DRAWINGS

FIG. 1 shows the Heat Sag versus the post cure temperature of variousRIM parts.

FIG. 2 shows the Izod Impact versus the post cure temperature.

FIG. 3 shows the Flexural Modulus versus the post cure temperature.

FIG. 4 shows the Flexural Modulus ratio at -20° F. and 325° F. versusthe post cure temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An object of this invention is to produce RIM polyurethane parts whichhave improved high temperature performance. For example, an automobileexterior body panel may be prepared by this invention which could beassembled on an automobile, painted and baked at 325° F. to cure thepaint. Prior art RIM polyurethane parts would distort at this high paintcuring temperature normally reserved for metal parts. However, the RIMparts prepared according to this invention remain stable even at thishigh temperature. Even more surprising, formulations prepared accordingto this invention exhibit excellent dimensional stability and stiffnessat temperatures of 325° F. or higher with no significant sacrifice inoverall properties and even display improved Izod impact properties.Prior art RIM polyurethane materials have been unable to withstand thesevere paint baking conditions that our materials endure without adverseeffect. Also, in softer RIM formulations for automotive fascia,significant improvement in 250° F. heat stability are observed when RIMparts are prepared according to this invention. Therefore, it is anobject of this invention to prepare RIM polyurethane elastomers havingsignificantly improved high temperature dimensional stability andstiffness.

It was surprisingly discovered that a significant improvement in hightemperature performance of RIM polyurethane elastomers was gained bycuring the demolded elastomers at about 290° F. to 425° F. andpreferably, from about 310° F. to 350° F. rather than the industrystandard of 250° F. As will be shown in the examples which follow, theimproved properties are noted with a wide variety of formulations.However, some formulations are particularly preferred because theirproperty improvements are outstanding even when compared to improvedparts made according to this invention. The preferred reactants for thisinvention are those which yield an isocyanate-chain extender reactionwith a high glass transition temperature. This glass transitiontemperature should be above the maximum ambient temperature to which thefinished product will be subjected. For example, a paint oven isnormally operated at about 325° F. The preferred polyols are those whichdo not significantly adversely affect the glass transition temperatureof the isocyanate-chain extender reaction.

The polyols useful in the process of this invention include polyetherpolyols, polyester diols, triols, tetrols, etc., having an equivalentweight of at least 500, and preferably at least 1000 up to about 3000.Those polyether polyols based on trihydric initiators of about 4000molecular weight and above are especially preferred. The polyethers maybe prepared from ethylene oxide, propylene oxide, butylene oxide ormixtures of propylene oxide, butylene oxide and/or ethylene oxide. Inorder to achieve the rapid reaction rates which are normally requiredfor molding RIM polyurethane elastomers, it is preferable that thepolyol be capped with enough ethylene oxide to increase the reactionrate of the polyurethane mixture. Normally at least 50% primary hydroxylis preferred, although amounts of primary hydroxyl less than this areacceptable if the reaction rate is rapid enough to be useful inindustrial application. Other high molecular weight polyols which may beuseful in this invention are polyesters or hydroxyl terminated rubbers(such as hydroxyl terminated polybutadiene). Hydroxyl terminatedquasi-prepolymers of polyols and isocyanates are also useful in thisinvention.

The chain-extenders useful in the process of this invention arepreferably difunctional. Mixtures of difunctional and trifunctionalchain-extenders are also useful in this invention. The chain-extendersuseful in this invention include diols, amino alcohols, diamines ormixtures thereof. Low molecular weight linear diols such as1,4-butanediol and ethylene glycol have been found suitable for use inthis invention. Ethylene glycol is especially preferred. Thesechain-extenders produce a polymer having a high glass transitiontemperature and/or high melting points when reacted with a suitablediisocyanate to be discussed below. It has been discovered that thepolyurethane polymers of this invention which have a high glasstransition temperature and a high melting point also show the improvedproperties in the process of this invention. Other chain-extendersincluding cyclic diols such as 1,4-cyclohexane diol and ring containingdiols such as bishydroxyethylhydroquinone, amide or ester containingdiols or amino alcohols, aromatic diamines and aliphatic amines wouldalso be suitable as chain-extenders in the practice of this invention.

A wide variety of aromatic polyisocyanates may be used here. Typicalaromatic polyisocyanates include p-phenylene diisocyanate, polymethylenepolyphenylisocyanate, 2,6-toluene diisocyanate, dianisidinediisocyanate, bitolylene diisocyanate, napthalene-1,4-diisocyanate,bis(4-isocyanatophenyl)methane, bis(3-methyl-3-isocyantophenyl)methane,bis(3-methyl-4-isocyanatophenyl)methane, and 4,4'-diphenylpropanediisocyanate.

Other aromatic polyisocyanates used in the practice of the invention aremethylene-bridged polyphenyl polyisocyanate mixtures which have afunctionality of from about 2 to about 4. These latter isocyanatecompounds are generally produced by the phosgenation of correspondingmethylene bridged polyphenyl polyamines, which are conventionallyproduced by the reaction of formaldehyde and primary aromatic amines,such as aniline, in the presence of hydrochloric acid and/or otheracidic catalysts. Known processes for preparing polyamines andcorresponding methylene-bridged polyphenyl polyisocyanates therefrom aredescribed in the literature and in many patents, for example, U.S. Pat.Nos. 2,683,730; 2,950,263; 3,012,008; 3,344,162 and 3,362,979.

Usually methylene-bridged polyphenyl polyisocyanate mixtures containabout 20 to about 100 weight percent methylene diphenyldiisocyanateisomers, with the remainder being polymethylene polyphenyl diisocyanateshaving higher functionalities and higher molecular weights. Typical ofthese are polyphenyl polyisocyanate mixtures containing about 20 to 100weight percent methylene diphenyldiisocyanate isomers, of which 20 toabout 95 weight percent thereof is the 4,4'-isomer with the remainderbeing polymethylene polyphenyl polyisocyanates of higher molecularweight and functionality that have an average functionality of fromabout 2.1 to about 3.5. These isocyanate mixtures are known,commercially available materials and can be prepared by the processdescribed in U.S. Pat. No. 3,362,979, issued Jan. 9, 1968 to Floyd E.Bentley.

By far the most preferred aromatic polyisocyanate is methylenebis(4-phenylisocyanate) or MDI. Pure MDI, quasi- are prepolymers of MDI,modified pure MDI, etc. Materials of this type may be used to preparesuitable RIM elastomers. Since pure MDI is a solid and, thus, ofteninconvenient to use, liquid products based on MDI are often used and areincluded in the scope of the terms MDI or methylenebis(4-phenylisocyanate) used herein. U.S. Pat. No. 3,394,164 is anexample of a liquid MDI product. More generally uretonimine modifiedpure MDI is included also. This product is made by heating puredistilled MDI in the presence of a catalyst. The liquid product is amixture of pure MDI and modified MDI: ##STR1## Examples of commercialmaterials of this type are Upjohn's Isonate 125M (pure MDI) and Isonate143L ("liquid" MDI).

The foam formulation includes a great number of other recognizedingredients usually present in the polyol blend, such as additionalcross-linkers--catalysts, extenders, blowing agents and the like.Blowing agents may include halogenated low-boiling hydrocarbons, such astrichloromonofluoromethane and methylene chloride, carbon dioxide,nitrogen, etc., used. Catalysts such as tertiary amines or an organictin compound or other polyurethane catalysts may be used. The organictin compound may suitably be a stannous or stannic compound, such as astannous salt of a carboxylic acid, a trialkyltin oxide, a dialkyltindihalide, a dialkyltin oxide, etc., wherein the organic groups of theorganic portion of the tin compound are hydrocarbon groups containingfrom 1 to 8 carbon atoms. For example, dibutyltin dilaurate, dibutyltindiacetate, diethyltin diacetate, dihexyltin diacetate,di-2-ethylhexyltin oxide, dioctyltin dioxide, stannous octoate, stannousoleate, etc., or a mixture thereof, may be used.

Tertiary amine catalysts include trialkylamines (e.g. trimethylamine,triethylamine), heterocyclic amines, such as N-alkylmorpholines (e.g.,N-methylmorpholine, N-ethylmorpholine, dimethyldiaminodiethylether,etc.), 1,4-dimethylpiperazine, triethylenediamine, etc., and aliphaticpolyamines, such as N,N,N'N'-tetramethyl-1, 3-butanediamine.

Other conventional formulation ingredients may also be employed, suchas, for example, foam stabilizers, also known as silicone oils oremulsifiers. The foam stabilizer may be an organic silane or siloxane.For example, compounds may be used having the formula:

    RSi[O--(R.sub.2 SiO).sub.n --(oxyalkylene).sub.m R].sub.3

wherein R is an alkyl group containing from 1 to 4 carbon atoms; n is aninteger of from 4 to 8; m is an integer of from 20 to 40; and theoxyalkylene groups are derived from propylene oxide and ethylene oxide.See, for example, U.S. Pat. No. 3,194,773.

Although not essential for the practice of this invention, the use ofcommonly known additives which enhance the color or properties of thepolyurethane elastomer may be used as desired. For example, chopped ormilled glass fibers, chopped or milled carbon fibers and/or othermineral fibers are useful.

The RIM polyurethane elastomers of this invention are made in theconventional manner in mold and are then post cured at temperatures ofabout 290° F. to 425° F. and preferably about 310° F. to 350° F.Unexpectedly, these high post curing temperatures increase the hightemperature stability of the finished RIM polyurethane elastomer. As thefollowing examples will show, the heat sag at 325° F. is improvedsubstantially at post cured temperatures above 290° F. Also,surprisingly, many formulations possessing this higher temperaturestability show no less and sometimes greater Izod impact resistance whencured at the high temperatures of this invention.

Another type of additive which may be required as post curingtemperatures approach 400° F. or more is an antioxidant. The materialswhich are well known to those skilled in the art include hinderedphenols as well as other materials.

In a particularly preferred embodiment of this invention, a highmolecular weight polyether polyurethane polyol of 5000 molecular weightor above is combined with ethylene glycol and standard catalysts systemis combined with 4,4'-diphenylmethane diisocyanate (MDI) along withother necessary ingredients known in the art and subjected to a normalRIM molding procedure. The reacted RIM part has been removed from themold and post cured at a temperature above 310° F. for about 30 minutes.As will be shown below such a procedure caused a striking improvement inheat sag over procedures of the prior art where lower post curedtemperature is used. Also, this particular formulation showed animprovement over other formulations although all formulations testeddisplayed an improvement as post cured temperature was increased.

The following examples demonstrate our invention. They are not to beconstrued as limiting our invention in any way but merely to beexemplary of the improvement and manner in which our invention may bepracticed.

A glossary of terms and materials used in the following examples followsthe examples.

EXAMPLE I

THANOL® SF-5505* (12.0 pbw), ethylene glycol (6.44 pbw), L 5430 siliconeoil (0.2 pbw), THANCAT® DMDEE (0.25 pbw), dibutyltin dilaurate (0.015pbw) and Foamrez UL-29 (0.025 pbw) were premixed and charged into theB-component working tank of an Admiral 40 lb. per min. low pressuremechanical mix foam machine. Isomate 143L (30.06 pbw) and P55-O quasiprepolymer (5.24 pbw) were premixed and charged into the A-componentworking tank. The A-component temperature was adjusted to 80° F. and theB-component temperature was adjusted to 120° F. The machine wascalibrated to deliver 4750 gms/min of B-component and 8870 gms/min ofA-component (isocyanate to hydroxyl ratio=1.05). The ingredients werethen mixed by a spiral type mixer turning at 4500 rpm and injected intoa 15 in. by 15 in. by 0.150 in. steel mold preheated to 145° F. througha gating system which was built into the mold. A 3.2 second shot yieldeda flat plaque having an overall density of about 62 pcf. Release timewas 45 seconds from pour.

Two identical plaques were prepared and one was post cured at 250° F.for 1/2 hour while the other was post cured at 325° F. for 1/2 hour.After a week's rest at 75° F. and 50% relative humidity, 1 in. by 6 in.samples were cut from each of the above plaques. The samples wereclamped at one end such that they projected horizontally with exactly4.0 inches of sample remaining unsupported. After 1/2 hour the distancefrom the unsupported end to the base of the clamping fixture wasmeasured. The fixture was then placed into a force draft oven at 325° F.for 30 minutes. After 30 minutes cooling, the distance from the end ofthe sample to the base of the clamping fixture was again measured. Thedifference in these two measurements (in inches) is termed the heat sag.The sample post cured at 325° F. exhibited a heat sag of 0.10 incheswhile the sample post cured at 250° F. exhibited a heat sag of 0.42inches. The heat sag was also determined for identical plaques whichwere post cured at these temperatures for one hour. The heat sags wereessentially identical to those obtained at 1/2 hour cure time. Fromthese experiments it was concluded that the high temperature post curecaused a striking improvement in heat sag. The heat sag is analagous topast serviceability at the measured temperature. It is one of thestandard tests for heat serviceability used by the automotive industry.

EXAMPLE II

The B-component of Example I was charged into the B-component workingtank of a Cincinnati Milacron LRM-2 impingement mix RIM machine. Isonate143L (29.0 pbw) and L55-O quasi prepolymer (5.63 pbw) were premixed andcharged into the A-component working tank. The A-component temperaturewas adjusted to 75° F. and the B-component temperature was adjusted to100° F. The machine was then set to deliver the components at aninjection rate of 3 lbs/sec and at a weight ratio of 0.546B-component/A-component. This represents an isocyanate index of 1.02.The components were then injected at an impingement pressure ofapproximately 900 psi into a steel plaque mold having cavity dimensionsof 0.125 inches by 24 inches by 48 inches. The mold temperature was setat 150° F. The parts were released in 60 seconds from pour. The plaqueshad a specific gravity of about 1.1.

A number of identical plaques were prepared and cured within 15 minutesfrom pour for 1/2 hour at temperatures ranging from 250° F. to 350° F.in 10° F. increments. After one week's rest at 75° F. and 50% relativehumidity, the heat sag of the samples cured at various temperatures weredetermined by the procedure outlined in Example I except an overhang of6 inches instead of 4 inches was used in order to subject the samples toa more severe test so that smaller variations in heat sag could be seen.The data are presented graphically in FIG. I. As can be seen from thefigure, the heat sag improved dramatically as the cure temperature isincreased with a leveling of the effect starting about 280° F. Allplaques were characterized by good dimensional stability upon removalfrom the cure oven (no significant distortion) until a cure temperatureof 350° F. was reached at which point the plaques distorted badly.

EXAMPLE III

The experiment in Example II was repeated except that a mixture ofIsonate 143L (28.61 pbw) and P55-O quasi prepolymer (5.54 pbw) wassubstituted for the A-component of Example II. In this case, theB-component to A-component ratio was set at 0.544 (1.02 isocyanateindex). The data are presented graphically in FIG. I. As can be seenfrom FIG. 1, this RIM elastomer responded to cure temperature in a verysimilar manner to Example II. The significant difference is that theheat sag does not reach as low a value as Example II.

EXAMPLE IV

The experiment in Example II was repeated except that a mixture ofIsonate 191 (28.52 pbw) and P55-O quasi prepolymer (5.53 pbw) wassubstituted for the A-component ratio was set at 0.556 (1.05 isocyanateindex). The data are presented graphically in FIG. I. As can be seenfrom FIG. I, this RIM elastomer responded to cure temperature in a verysimilar manner to Examples II and III. The significant difference isthat the heat sag does not reach as low a value as in Example II or III.

EXAMPLE V

The experiment in Example II was repeated at 250°, 300° and 340° F. postcure temperatures except that the chain-extender in the B-component was1,4-butanediol (9.35 pbw). In this case, the B-component to A-componentweight ratio was set at 0.631 (1.02 isocyanate index). The data arepresented graphically in FIG. I. As can be seen from FIG. I, this RIMelastomer responded to cure temperature in a very similar manner toExamples II, III and IV. The significant difference is that the heat sagdoes not attain as low a value as in Examples II, III or IV. It shouldbe noted, however, that the heat sag (cured at 325° F.) measured at 250°F. on a 4 inch sample (industry standard) are excellent (0.03 in.).Thus, this system is no doubt excellent for lower temperatureapplications.

EXAMPLE VI

The experiment in Example II was repeated at 250°, 270°, 290°, 310°,330° and 350° F. post cure temperatures except that a mixture of Papi901 (27.58 pbw) and P55-O (5.35 pbw) was substituted for the A-componentof Example II. In this case, the B-component to A-component ratio wasset at 0.575 (1.05 isocyanate index). The data are presented graphicallyin FIG. I. As can be seen from FIG. I, this RIM elastomer responded tocure temperature similarly to Examples II, III, IV and V except that theimprovement in heat sag obtained by high temperature cure is much lessthan in the other examples. It should also be noted that this elastomeris characterized by the poorest heat sag of all the elastomers tested.

More extensive testing was done on Examples II through VI. The followingtable is a summary of results.

    __________________________________________________________________________    Property     Example II                                                                              Example III                                                                             Example IV                                                                              Example V Example                  __________________________________________________________________________                                                         VI                       Cure T, °F.                                                                         250  330  250  330  250  320  250  350  250  310                 Isocyanate Index                                                                           1.02 1.02 1.02 1.02 1.05 1.05 1.02 1.02 1.05 1.05                Heat sag, in 6" overhand                                                                   2.2  0.5  2.6  0.7  3.0  1.0  >4   2.0  3.3  2.4                 Izod Impact, ft. lb/in.                                                                    6.5  7.6  7.3  7.4  5.3  4.6  6.3  4.6  3.2  2.8                 notch                                                                         Tensile, psi 5000 5070 4900 5100 5500 5700 4170 4450 5300 5500                Elongation, %                                                                              123  127  133  138  106  97   128  93   63   67                  Tear, pli    630  570  650  590  605  530  728  513  488  482                 Flexural modulus,                                                             psi × 10.sup.3                                                           (a) 75° F.                                                                         147.0                                                                              146.7                                                                              136.5                                                                              129.8                                                                              157.3                                                                              151.3                                                                              124.6                                                                              124.2                                                                              158.4                                                                              158.9                (b) -20° F.                                                                        254.0                                                                              236.8                                                                              263.1                                                                              231.9                                                                              274.2                                                                              231.5                                                                              253.6                                                                              199.5                                                                              283.9                                                                              271.4                (c) 158° F.                                                                        82.0 93.8 75.1 86.1 87.5 92.2 59.9 76.5 87.0 91.7                 (d) 325° F.                                                                        24.1 40.4 23.1 27.0 14.1 26.7 --   7.2  4.4  9.1                 Flexural modulus ratio                                                         b/c         3.1  2.5  3.5  2.7  3.1  2.5  4.2  2.6  3.3  3.0                  b/d         10.5 5.9  11.4 8.6  19.5 8.7  --   27.7 64.5 29.8                __________________________________________________________________________

Study of the above table clearly shows that the isocyanate-chainextender reaction product and post cure temperatures have a dramaticeffect on the properties of the resulting RIM elastomer. Generally,within each example, properties are better for the elastomers cured athigher temperature. This is especially true of the thermal properties(heat sag, flexural moduli and flexural modulus ratios). The elastomerscured at higher temperatures are more resilient (lower -20° F. flexuralmodulus) at low temperature and stiffer at high temperature (high 158°and 325° F. flexural modulus). The elastomers cured at highertemperatures also show less temperature sensitivity in flexural modulus(lower flexural modulus ratios). It is clear from the table that theabsolute magnitude of the physical properties, especially the thermalproperties, is partially controlled by the isocyanate chain-extenderreaction product, properly post cured (post cured at highertemperature). Examples II and III are preferred. The other examples showless improvement. From these considerations, it is evident that theisocyanate in the A-component should be relatively pure and either haveor possess the capability of approaching a functionality of 2.0. Also,it is evident that the chain extender employed has a great effect onfinal heat properties. The RIM elastomer of Example V is less heatstable than the one of Example II. Prolonged post cure time or higherpost cure temperature might make the RIM elastomer in Example Vacceptable in heat properties.

FIG. II graphically presents the behavior of Izod Impact as a functionof cure temperature and the composition of the isocyanate chain-extenderreaction product. It is clear from FIG. II that in some cases, the IzodImpact increases with increasing cure temperature (Example II) in somecases it decreases with increasing cure temperature (Examples IV and V)and in some cases remains rather constant (Examples III and VI). Also,the magnitude of the highest Izod Impact value attainable within anexample seems to be a function of chain extender and isocyanate. Again,Examples II and III are preferred in this invention. From theseconsiderations, it is again evident that the isocyanate in theA-component should be relatively pure and either have or possess thecapability of approaching a functionality of 2.0. Also, the chainextender selected is critical to the final Izod Impact achieved.

In FIG. III, the flexural modulus at 325° F. is presented graphically asa function of cure temperature. These data correlate to the heat sagdata in FIG. I. The higher the flexural modulus at 325° F., the lowerthe heat sag measured at 325° F. Also, it is apparent that the chainextender and isocyanate chosen to form the isocyanate chain-extenderreaction product is as important as the cure temperature. The sameconclusions are drawn from this figure as far as selection of onetemperature, chain extender and isocyanate are concerned as have beendrawn from analysis of the data in FIGS. I and II.

In FIG. IV, the Flexural Modulus Ratio (-20° F./325° F.) as a functionof cure temperature is presented graphically. These data show theimportance of cure temperature and selection of isocyanate andchain-extender with respect to changes in Flexural Modulus. The lowerthe Flexural Modulus Ratio the less sensitive is the flexural modulus tochanges in temperature. The same conclusions are drawn from this figureas drawn from FIGS. I-III.

EXAMPLE VII

The experiment of Example II was repeated except that the THANOL SF-5505level was increased from 12 pbw to 16 pbw. This changed the flexuralmodulus at room temperature from about 140,000 psi (Example II) to about90,000 psi (Example VII). The 6 inch heat sag at 325° F. for 1/2 hourwas determined on samples cured at 250° F. (73.5 in.) and 325° F. (0.6in.). Thus, the heat stability of the elastomer increased dramatically(lower heat sag) when cured at the higher temperature. This experimentextends the practice of our invention to lower flexural modulus RIMelastomers.

EXAMPLE VIII

The experiment of Example II was repeated with the followingformulation:

    ______________________________________                                                          A-Component                                                 B-Component       (1.02 Isocyanate Index)                                     ______________________________________                                        THANOL SF-6503, 13.5 pbw                                                                        Isonate 143L, 26.32 pbw                                     Ethylene Glycol, 6.44 pbw                                                                       P-55-0 (quasi-prepolymer)                                                     5.21 pbw                                                    Dibutyl tin dilaurate,                                                        0.04 pbw                                                                      ______________________________________                                    

A sample cured at 325° F. for 1/2 hour exhibited a 4 inch heat sag(determined at 325° F. for 1/2 hour) of 0.15 inches while a sample curedat 250° F. for 1/2 hour had a heat sag (determined as above) of 0.93inches. The purpose of this experiment was to extend our invention to adifferent polyol (THANOL SF-6503) which has a higher molecular weightthan THANOL SF-5505.

EXAMPLE IX

The experiment of Example I was repeated with the following formulation:

    ______________________________________                                                           A-Component                                                B-Component        (0.98 Isocyanate Index)                                    ______________________________________                                        Experimental 4,000     Isonate 143L 28.9 pbw                                  molecular weight diol  L (5145-85)-0                                           (5145-85),  12 pbw    quasi prepolymer                                                                            5.6 pbw                                  Ethylene glycol                                                                            6.44 pbw                                                         L5430 Silicone oil                                                                         0.2 pbw                                                          THANCAT DMDEE                                                                              0.25 pbw                                                         Foamez UL29  0.025 pbw                                                        Dibutyl tin dilaurate                                                                      0.015 pbw                                                        ______________________________________                                    

A sample cured at 325° F. for 1/2 hour exhibited a 4 inch heat sag(determined at 325° F. for 1/2 hour) of 0.02 inches while a sample curedat 250° F. for 1/2 hour had a heat sag (determined as above) of 0.42inches. These results indicate that polyether polyols having a differentinternal structure are useful for this invention. The 5145-85experimental diol is a 4,000 molecular weight diol based on mixtures ofbutylene oxide and ethylene oxide and capped with ethylene oxide toyield a primary hydroxyl content of about 90%.

EXAMPLE X

The experiment of Example II was repeated with the followingformulation:

    ______________________________________                                                           A-Component                                                B-Component        (1.02 Isocyanate Index)                                    ______________________________________                                        THANOL SF-6503                                                                             100 pbw   Isonate 143 L                                                                             128.8 pbw                                  Ethylene glycol                                                                            25.6 pbw                                                         Dibutyl tin dilaurate                                                                      0.2 pbw                                                          Fluorocarbon 11-B                                                                          2.0 pbw                                                          ______________________________________                                    

Samples of the above elastomer cured at 325° F. for 1/2 hour exhibited a6 inch heat sag (325° F. for 1/2 hour) of 1.3 inches while those curedat 250° F. for 1 hour had a heat sag (same conditions as above) ofgreater than 3.5 inches. This example demonstrates the utility of thisinvention in improving the high temperature properties of RIM elastomershaving an intermediate flexural modulus (about 60,000 psi).

EXAMPLE XI

The experiment of Example I was repeated with the following formulation:

    ______________________________________                                                           A-Component                                                B-Component        (0.98 Isocyanate Index)                                    ______________________________________                                        THANOL SF-5505                                                                             16 pbw    Isonate 143L                                                                              28.5 pbw                                   Ethylene glycol                                                                            5.0 pbw   L-55-0 quasi                                                                  prepolymer  5.52 pbw                                   Monoethanolamine                                                                           1.44 pbw                                                         L5430 Silicone Oil                                                                         0.2 pbw                                                          THANCAT DMDEE                                                                              0.25 pbw                                                         Foamez UL29  0.025 pbw                                                        Dibutyl tin dilaurate                                                                      0.015 pbw                                                        ______________________________________                                    

The above formulation reacted too rapidly to mold a complete plaque onthis low pressure foam machine. A partial plaque was cut into twopieces. One piece was cured for 1/2 hour at 325° F. and the other piecewas cured for 1/2 hour at 250° F. The 325° F. cured piece exhibited aheat sag (6 inch overhang heated for 30 minutes at 325° F.) of 0.6inches while the piece cured at 250° F. had a heat sag (same conditionsas above) of 2.5 inches. This experiment demonstrates the utility ofstill another chain-extender, monoethanolamine, in the practice of thisinvention. Monoethanolamine has one primary amine per molecule and is anexample of a urea linkage forming chain extender.

GLOSSARY OF TERMS AND MATERIALS

RIM--Reaction Injection Molding

Polyol--A di or greater functionality high molecular weight alcohol oramine terminated molecule composed of ether groups such as ethylene,propylene, butylene, etc., oxides.

MDI--4,4' diphenyl methane diisocyanate

Isonate 143L--Pure MDI isocyanate modified so that it is a liquid attemperatures where MDI crystallizes--product of the Upjohn Co.

PAPI 901--A crude form of MDI containing about 30% higher functionalityisocyanates and other impurities--product of the Upjohn Co.

Isonate 191--Thought to be a 50/50 blend of Isonate 143L and PAPI901--product of the Upjohn Co.

Quasi-prepolymer L-55-0--A quasi-prepolymer formed by reacting weightsof Isonate 143L and THANOL SF-5505.

Quasi-prepolymer P-55-0--A quasi-prepolymer formed by reacting equalweights of PAPI 901 and THANOL SF-5505.

Quasi-prepolymer L-(5145-85)-0--A quasi-prepolymer formed by reactingequal weights of Isonate 143L and experimental polyol 5145-85.

THANOL SF-5505--a 5500 molecular weight polyether triol containingapproximately 80% primary hydroxyl groups.

THANOL SF-6503--A 6500 molecular weight polyether triol containingoxyethylene groups and approximately 90% primary hydroxyl groups.

L5430 Silicone Oil--A silicone glycol copolymer surfactant containingreactive hydroxyl groups. Product of Union Carbide.

THANCAT DMDEE--Dimorpholinodiethylether

Foamurez UL-29--A stannic diester of a thiol acid. The exact compositionis unknown. Product of Witco Chemical Co.

Fluorocarbon 11-B--An inhibited trichlorofluoromethane.

We claim:
 1. A method of making a foamed polyurethane elastomer ofimproved properties which comprises injecting via a RIM machine into amold cavity of the desired configuration a foam formulation, demoldingthe molded article and post curing the demolded article at a temperaturefrom about 290° F. to 425° F. for a time sufficient to achieve animprovement in properties said formulation being the reaction product ofan aromatic polyisocyanate, a polyol of above about 500 equivalentweight and a chain-extending agent comprising a low molecular weightactive hydrogen containing component of at least two (2) functionalitywherein the polyisocyanate and chain-extender are chosen from productswhich yield an isocyanate chain-extender reaction product with a glasstransition temperature of above about 325° F. and wherein the polyol ischosen from those products which do not significantly adversely affectthe glass transition temperature of the isocyanate chain-extenderreaction product.
 2. A method of claim 1 wherein said chain-extendingagent comprises ethylene glycol.
 3. A method of claim 1 wherein saidaromatic polyisocyanate is 4,4'-diphenylmethane diisocyanate.
 4. Amethod of claim 1 wherein said polyol is a diol or triol having anequivalent weight of from about 1000 to about 3000 and contains at leastabout 50 percent primary hydroxyl groups.
 5. The method of claim 1wherein said polyol is a polyether polyol.
 6. In a method for making apolyurethane elastomer of improved properties wherein a polyol of aboveabout 500 equivalent weight, an aromatic polyisocyanate and achain-extending agent comprising a low molecular weight active hydrogencontaining compound of at least two (2) functionality is injected into amold cavity of the desired configuration wherein the polyisocyanate andchain-extender are chosen from products which yield an isocyanatechain-extender reaction product with a glass transition temperature ofabove about 325° F. and wherein the polyol is chosen from those productswhich do not significantly adversely affect the glass transitiontemperature of the isocyanate chain-extender reaction product wherein amolded article is formed the improvement which comprisespost curing themolded article at a temperature of about 290° F. to 425° F. for a timesufficient to achieve an improvement in properties.
 7. In a method formaking a polyurethane elastomer of improved properties wherein a polyolof above about 500 equivalent weight, an aromatic polyisocyanate and achain-extending agent comprising a low molecular weight active hydrogencontaining compound of at least two (2) functionality is injected into amold cavity of the desired configuration wherein the polyisocyanate andchain-extender are chosen from products which yield an isocyanatechain-extender reaction product with a glass transition temperature ofabove about 325° F. and wherein the polyol is chosen from those productswhich do not significantly adversely affect the glass transitiontemperature of the isocyanate chain-extender reaction product wherein amolded article is formed the improvement which comprisespost curing themolded article at a temperature of about 310° F. for a time sufficientto achieve an improvement in properties.
 8. A method of making a foamedpolyurethane elastomer of improved properties which comprises injectingvia a RIM machine into a mold cavity of the desired configuration a foamformulation, demolding the molded article and post curing the demoldedarticle at a temperature from about 310° F. to 350° F. for a timesufficient to achieve an improvement in properties said formulationbeing the reaction product of an aromatic polyisocyanate, a polyol ofabove about 500 equivalent weight and a chain-extending agent comprisinga low molecular weight active hydrogen containing component of at leasttwo (2) functionality wherein the polyisocyanate and chain-extender arechosen from products which yield an isocyanate chain-extender reactionproduct with a glass transition temperature of above about 325° F. andwherein the polyol is chosen from those products which do notsignificantly adversely affect the glass transition temperature of theisocyanate chain-extender reaction product.
 9. A method of claim 8wherein said chain-extending agent comprises ethylene glycol.
 10. Amethod of claim 8 wherein said aromatic polyisocyanate is4,4'-diphenylmethane diisocyanate.
 11. A method of claim 8 wherein saidpolyol is a diol or triol having an equivalent weight of from about 1000to about 3000 and contains at least about 50 percent primary hydroxylgroups.
 12. The method of claim 8 wherein said polyol is a polyetherpolyol.